While embodiments are described below in relation to MBMS as implemented in LTE, the invention finds application also in other cellular radio networks such as WCDMA, GSM, CDMA etc, but may also be applicable in other type of networks implementing broadcast services.
Multimedia Broadcast Multicast Service (MBMS) for Long Term Evolution (LTE) networks is available in the 3GPP standard from release 9. An overview of the MBMS system is given in chapter 15 in the 3GPP technical specification TS 36.300.
The Mobility Management Entity (MME) and MBMS Gateway (GW) are connected via the Sm interface as described in 3GPP technical specification TS 23.246.
When a new session is about to start, the MBMS GW sends control plane messages to the MME containing information regarding the service, such as Quality of Service (QoS) profile. The QoS profile comprises, amongst other things the Maximum Bit Rate (MBR) and the Guaranteed Bit Rate (GBR) for the service in the MBMS Service Area. This message is the MBMS Session Start Request as specified in the 3GPP technical specification TS 29.274, section 7.13.1. The MME signals to the Multi-cell/multicast Coordination Entity (MCE) over the M3 interface that a new session starts using the MBMS Session Start Request message, this message is describe in 3GPP TS 36.444. The MCE controls a Multimedia Broadcast multicast service Single Frequency Network (MBSFN) area, normally consisting of cells belonging to several eNBs.
The MBMS transmissions are synchronized over the MBSFN area. That is, over the MBSFN area, possibly comprising several different eNBs and several different cells, all transmission should be simultaneous.
The MCE sends the MEMS Session Start Request message to the eNBs in its MBSFN area, as specified in 3GPP TS 36.443. The eNB's prepare resources for receiving user data according to the received information. User data received over M1 for the session is then broadcasted in the MBSFN area by the eNBs.
In release 9, there is an assumption that MBR equals GBR. For MBMS that means that resources have to be allocated for transmitting data at the maximum bit rate.
This has the drawback that for two services that has MBR=GBR=100, the total amount of resources that has to be allocated is 100+100=200.
To mitigate this problem MBMS shall, in later releases, exploit statistical multiplexing in order to more efficiently use the available resources. This means that since bitrates for services normally varies over time. Two services with MBR=150 and GBR=70 may, depending on the requirements, only require resources to carry the total bit rate 160.
The information provided to the MCE useful for admission control is MBR, GBR and the QCI (QoS Class Identifier) within the QoS IE. The currently standardized QCI parameters are found in Table 6.1.7 in 3GPP technical specification TS 23.203, and shows that different services accept different time delays and packet loss rates.